With increasing development of image processing technologies, image scanners become essential peripheral devices of the computer system and are used for scanning documents. The images of the scanned documents can be converted into digital files, which can be stored in, transmitted to or further processed by the computer, or otherwise directly printed.
Generally, flatbed image scanners are the widely used image scanners. The flatbed image scanners are advantageous because most documents can be scanned by such flatbed image scanners regardless of a single sheet or a thick book. However, the volume of the flatbed image scanner may occupy much working space, which is adverse to space utilization. In addition to increased image quality of the scanned document, the image scanners are designed and developed toward small size and light weightiness.
Since most documents to be scanned have specified sizes or conform to specified specifications, a certain planar area for the image scanner is inevitable. In order words, for a purpose of shrinking volume or decreasing weight of the image scanner, it is necessary to reduce the thickness of the image scanner. As a consequence, a so-called slim type image scanner is developed. On the other hand, an image scanner principally comprises a scanning module, which has a photosensing function and movable along the scanning direction to scan the document. Since this scanning module occupies much space of the image scanner, it is required to shrink the volume of the scanning module when the slim type image scanner is designed.
Referring to FIG. 1, a schematic cross-sectional view of a conventional scanning module 100 is illustrated. As shown in FIG. 1, in the rectangular housing 11 of the conventional scanning module 100, a light source 12, a reflective mirror set 13, an optical lens 14 and an image sensor 15 are provided. An exemplary optical sensor 15 of the scanning module 100 includes a charge couple device (CCD), a CMOS sensing element and the like. The process for performing a scanning operation will be illustrated as follows. Firstly, the light emitted by the light source 12 is projected onto a document 102, which is placed on a transparent platform 101. The light reflected from the scanned document 102 is reflected by the reflective mirror set 13, and then focused by the optical lens 14. The focused light is then imaged onto the image sensor 15 to convert the optical signals into analog electrical signals. In this conventional technology, the reflective mirror set 13 is fixed within the scanning module 100. The reflective mirror set 13 includes plural reflective mirrors, which are hooked on the rectangular housing 11 by means of corresponding plastic hooking elements integrally formed on the rectangular housing 11. Due to mechanical precision tolerance during the process of fabricating these hooking elements, these reflective mirrors may have inherent angle deviation. As known, the inherent angle deviation may adverse affect the optical path resulted from the plural reflective mirrors.
If the volume of the scanning module is huge enough, the influence of the angle deviation is relatively small and the optical path is not considerably affected. Whereas, in a case that a slim type image scanner or a slim type scanning module is designed, any tiny reflective angle deviation may seriously or adversely affect the optical path associated with the scanned image of the document. Therefore, when the slim type scanning module is designed, the angle deviation needs to be taken into consideration and thus a suitable reflective mirror adjustable mechanism is provided to minimize the influence of the angle deviation.
In a co-pending Taiwanese Patent Application No. 94133457, entitled “Scanning module of image scanner”, which was filed by the same assignee of the present application and the contents of which are hereby incorporated by reference, a method and a device for solving the above problems are disclosed. Please refer to FIGS. 2(a) and 2(b), which are schematic perspective and side views of the scanning module 200 of this co-pending application, respectively. For clarity and neat drawing, however, only one reflective mirror is shown in the drawing. As shown in FIG. 2(a), a screw hole 22 and a screw 23 are provided at a side wall 211 of the rectangular housing 21 of the scanning module 200. The screw 23 is penetrated through the screw hole 22. The locations of a hooking element 24 and a reflective mirror 25 inside the rectangular housing 21 corresponds to those of the screw hole 22 and the screw 23. If the actual reflective optical path B is deviated from the ideal reflective optical path A, the assembler may rotate the screw 23 to adjust the reflective angle of the reflective mirror 25 due to the tiny shift of the screw 23. The deviation between the actual reflective optical path B and the ideal reflective optical path A is also illustrated in FIG. 2(b).
Although this reflective mirror adjustable mechanism may adjust the reflective angle and the reflective optical path of the reflective mirror 25, there are still some drawbacks. For example, since the length of the screw 23 needs to be shrunk when the slim type scanning module is designed, fine tuning or precisely tuning is impossible. In other words, coarse tuning of the reflective mirror adjustable mechanism is permissible because the rotational degree of the screw 23 is limited. In addition, according to cooperation of the screw 23 and the hooking element 24, the reflective mirror adjustable mechanism is adjustable along a single direction rather than the reverse direction.
In views of the above-described disadvantages of the prior art, the applicant keeps on carving unflaggingly to develop an improved scanning module of an image scanner according to the present invention through wholehearted experience and research.